Surface lighting device and portable terminal using the same

ABSTRACT

A surface lighting device has one single light source and a light-guide-board. The board includes a light-guiding-section and a light-emitting-section. A shorter side of the light-guiding-section is not more than 8 mm, and an area of the light-emitting-section is not less than 500 mm 2 . The light-emitting-section has the following features: (1) a ratio of min. luminance vs. max. luminance is not less than 0.3; (2) an average luminance ranges from 1 cd/m 2  to 200 cd/m 2 , and (3) a change in luminance per unit length is not more than (average luminance)×100 cd/m 3 . Employing plural light-emitting-elements in one light source allows the lighting device to produce versatile colors. The light source, light-guide-board and a holder are structured and shaped in optimum way, so that unevenness in luminance of the device is reduced. An LCD unit incorporating this surface lighting device increases its display quality, and a portable terminal incorporating this LCD unit produces easy-to-lead display.

FIELD OF THE INVENTION

The present invention relates to surface lighting devices for liquidcrystal displays, and more particularly it relates to surface lightingdevices having light emitting diodes and the like for lighting thedisplays as well as for portable terminals using the surface lightingdevices.

BACKGROUND OF THE INVENTION

Surface lighting devices have been used for backlighting of liquidcrystal displays (LCD) employed in cellular-phones, portable terminalsand the like. Light emitting diodes (LED) in chip-shape have been usedas light sources of this surface lighting device because of LED's smallsize and low power consumption. Lately, LEDs replace cold-cathode tubesas surface lighting devices of various portable-terminals includinginformation terminals, digital cameras, camcorders because LEDs aresuperior in smaller size, longer battery life, and withstanding shocks.

Various structures are available in those conventionalsurface-lighting-devices using LEDs. For instance, Japanese PatentExamined Application Publication No. H03-32075 discloses that LEDs aredisposed behind an LCD panel thereby emitting light directly to the backface of the LCD panel in order to light the panel. However, thinnerbodies of the terminals are required in the market, and problems ofdisposing electronic circuits behind LCD elements are not favorable forthis structure, i.e. a structure where LEDs are disposed directly behindthe LCD panel becomes inconvenient. Therefore, fewer models of cellularphones and the like use this structure as the surface lighting devicefor LCD.

Regarding the surface lighting device for LCDs of cellular phones, LEDsare disposed outside the display face of LCD elements in many cases. Forinstance, Japanese Patent Examined Application Publication No. H05-21233teaches that LEDs are disposed outside the display face of LCD elementsso that the light of the LEDs is guided under the LCD elements by usinga reflective face and a resin board.

However, the conventional surface lighting device as discussed abovedistributes uneven luminance, i.e. the light is distributed notuniformly if only one LED is provided at the center of the device. Inthis case, neighbor of the LED is only well-lighted, and periphery ofthe LED is poorly-lighted. Such luminance distribution becomes moreobvious at a greater area to be lighted. This uneven luminancedistribution would result in poor readability of the display, andfurther, produce an unrecognizable displayed section due to poor-light.To overcome this problem, a number of LEDs as a light source isincreased, and spaces between the LEDs arrayed are narrowed, so that theluminance distribution is improved. This is a conventional measureagainst the problem.

When the number of LEDs is increased in the surface lighting device ofthe LCD used in cellular phones and other portable terminals, it notonly boosts the power consumption, but also incurs complicated works formounting the LEDs as well as a cost increase.

When a plurality of LEDs are used, differences between wavelengths oflights emitted from the LEDs produce an uneven color. To be morespecific, in many cases, each LED differs in a light wavelength emittedtherefrom by several nano-meters due to individual characteristics. Sucha little difference; however, produces great unevenness in a color forhuman eyes when respective areas illuminated by each LED and theirborders are compared each other. In order to eliminate the unevenness ina color, emit each LED and measure the light wavelength, therebycollecting the LEDs having the same wavelength. This operation isrequired to assemble one surface lighting device free from a dispersionof the light wavelengths. This operation; however, requires a cumbersome100% inspection on the LEDs, and this is one of the causes to lower theproductivity of the surface lighting devices.

Also, luminance differences among the LEDs due to individualcharacteristics produce uneven luminance of the surface lighting device.

Another method for improving the unevenness in a color and luminance isto use one LED, and a light guiding section of a light guide board iselongated so that light can be scattered sufficiently. Then the light isemitted from a light emitting section. This method; however, limits thedownsizing of the surface lighting devices.

SUMMARY OF THE INVENTION

A surface lighting device has the following structure:

-   -   one light source;    -   a light guiding section having a length not more than 8 mm in        the minor axis direction;    -   a light emitting area of a light guide member being not less        than 500 mm²;    -   a ratio of minimum luminance vs. maximum luminance, being not        less than 0.3;    -   an average luminance ranging between 1cd/m² and 200 cd/m²; and    -   a change amount per unit length in luminance of a light emitting        section being not more than the value of (the average        luminance)×100 cd/m³.

Another structure is available as follows:

-   -   a light guiding section having a length not more than 8 mm in        the minor axis direction;    -   a light emitting area of a light guide member being not less        than 500 mm²;    -   one light element out of plurality of light elements being        emitted anytime and the other light element s are emitted        independently on demand;    -   a ratio of a min luminance vs. a max. luminance being not less        than 0.3;    -   an average luminance ranging between 1cd/m² and 200 cd/m²; and    -   a change amount per unit length in luminance of a light emitting        section being not more than the value of (the average        luminance)×100 cd/m³.

A portable terminal of the present invention comprises the followingelements:

-   -   a display device having the surface lighting device at a lower        part thereof;    -   a converter for converting at least one of a data signal or an        audio signal into a transmission signal, or converting a        received signal into at least one of a data signal or an audio        signal;    -   an antenna for receiving the transmission signal and the        received signal; and    -   a controller for controlling the respective parts discussed        above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a surface lighting device in accordance with afirst exemplary embodiment of the present invention.

FIG. 2 is a lateral view of the surface lighting device in accordancewith the first exemplary embodiment of the present invention.

FIG. 3 is a perspective view of a light guide board in accordance withthe first exemplary embodiment of the present invention.

FIG. 4 is a perspective view of a holder in accordance with the firstexemplary embodiment of the present invention.

FIG. 5 is a cross section of a neighbor of a barrier plate in accordancewith the first exemplary embodiment of the present invention.

FIG. 6 is a perspective view of a holder in accordance with a secondexemplary embodiment of the present invention.

FIG. 7 is a cross section of a neighbor of a barrier plate in accordancewith the second exemplary embodiment of the present invention.

FIG. 8 is a cross section of a neighbor of a barrier plate in accordancewith the third exemplary embodiment of the present invention.

FIG. 9 is a cross section of a neighbor of a barrier plate in accordancewith the fourth exemplary embodiment of the present invention.

FIG. 10 is a plan view of a surface lighting device in accordance withthe fourth exemplary embodiment of the present invention.

FIG. 11 is a plan view of a portable terminal in accordance with anexemplary embodiment of the present invention.

FIG. 12 is a block diagram of a portable terminal in accordance with anexemplary embodiment of the present invention.

FIG. 13 is a partial cross section of a portable terminal in accordancewith an exemplary embodiment of the present invention.

FIG. 14 is a perspective view of an LED of a surface lighting device inaccordance with the first exemplary embodiment of the present invention.

FIG. 15 illustrates light intensity distribution of the LED used in asurface lighting device in accordance with the first exemplaryembodiment of the present invention.

FIG. 16 is a perspective view of an LED in accordance with the firstexemplary embodiment of the present invention.

FIG. 17 is a CIExy color atlas in accordance with an exemplaryembodiment of the present invention.

FIG. 18 is a front view of a surface lighting device in accordance withan exemplary embodiment of the present invention.

FIG. 19 is a cross section of a surface lighting device in accordancewith an exemplary embodiment of the present invention.

FIG. 20 is a front view of a light guide board in accordance with anexemplary embodiment of the present invention.

FIG. 21 illustrates positions of an LED having a plurality of lightemitting elements and a light guiding section in accordance with anexemplary embodiment of the present invention.

FIG. 22 illustrates positions of an LED having a plurality of LEDs and alight guiding section in accordance with an exemplary embodiment of thepresent invention.

FIG. 23 is a cross section of neighbor of an LED in accordance with anexemplary embodiment of the present invention.

FIG. 24 is a front view of a surface lighting device in accordance withan exemplary embodiment of the present invention.

FIG. 25 is a cross section of a surface lighting device in accordancewith an exemplary embodiment of the present invention.

FIG. 26 is a front view of a surface lighting device in accordance withan exemplary embodiment of the present invention.

FIG. 27 is a front view of a portable terminal in accordance with anexemplary embodiment of the present invention.

FIG. 28 is a perspective view of a portable terminal in accordance withan exemplary embodiment of the present invention.

FIG. 29 is a front view of a surface lighting device in accordance withan exemplary embodiment of the present invention.

FIG. 30 is a front view of a surface lighting device in accordance withan exemplary embodiment of the present invention.

FIG. 31 is a cross section of a surface lighting device in accordancewith an exemplary embodiment of the present invention.

FIG. 32 is a front view of a surface lighting device in accordance withan exemplary embodiment of the present invention.

FIG. 33 is a lateral view of an LED in accordance with an exemplaryembodiment of the present invention.

FIG. 34 is a graph illustrating relative light intensities emitted froman LED in accordance with an exemplary embodiment of the presentinvention.

FIG. 35 is a front view of a light guide board in accordance with anexemplary embodiment of the present invention.

FIG. 36 is a front view of a surface lighting device in accordance withan exemplary embodiment of the present invention.

FIG. 37 is a cross section of a surface lighting device in accordancewith an exemplary embodiment of the present invention.

FIG. 38 is a front view of a surface lighting device in accordance withan exemplary embodiment of the present invention.

FIG. 39 is a front view of a portable terminal in accordance with anexemplary embodiment of the present invention.

FIG. 40 is a cross section of a portable terminal in accordance with anexemplary embodiment of the present invention.

FIG. 41 is a front view of a surface lighting device in accordance withan exemplary embodiment of the present invention.

FIG. 42 illustrates characteristics illustrating a relation between anangle forming a sixth side of a surface lighting device and unevenluminance in accordance with an exemplary embodiment of the presentinvention.

FIG. 43 is a block diagram illustrating a portable terminal inaccordance with an exemplary embodiment of the present invention.

FIG. 44 is a front view of a surface lighting device in accordance withan exemplary embodiment of the present invention.

FIG. 45 is a cross section of a surface lighting device in accordancewith an exemplary embodiment of the present invention.

FIG. 46 is a front view of a surface lighting device in accordance withan exemplary embodiment of the present invention.

FIG. 47 is a graph illustrating relative light intensity emitted from anLED in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Exemplary Embodiment 1

The first exemplary embodiment is demonstrated hereinafter withreference to FIG. 1 through FIG. 5.

In FIG. 1, a light source in small size such as a midget-light-bulb oran LED is employed as light source 1. More specifically, a spotlight-source defined as follows is preferably employed: a volume is notmore than 12 mm³, a thickness is not more than 2 mm, and a lightemitting area is not more than 2.8 mm². A highly-efficient LED, inparticular, satisfying the definition discussed above produces luminancein more even distribution, thereby realizing an easy-to-see surfacelighting device. The embodiment demonstrated hereinafter employs an LEDas light source 1. Cellular phones and portable-information-terminals,both are small in size, require a ultra tiny and thin light source, andLED 1 is thus preferably not more than 3 mm³ in volume. In this case, ifLED 1 is mountable directly onto a circuit board, it saves cumbersomewiring and improves the manufacturing productivity.

The surface lighting device employing one single LED can reduce thepower consumption, thereby being suitable for portable apparatuses. Theconstruction of employing one single LED is free from uneven colors aswell as uneven luminance caused by different light wavelengths and adisperse of light emitting efficiency caused by a plurality of LEDs.This eliminates screening of LEDs thereby substantially increasing theproductivity of the surface lighting device and lowering the cost.

Another preferable structure of LED 1 is demonstrated with reference toFIG. 14 and FIG. 15.

FIG. 14 is a perspective view of a light source of the surface lightingdevice in the first embodiment, and FIG. 15 illustrates an intensitydistribution of the light emitted from the LED used as the light source.In FIG. 14, light emitting element 1 a is surrounded by lens 1 b and ismounted onto base substrate 1 c. Lens 1 b is preferably made of epoxyresin because the epoxy resin is highly light transparent and withstandsa high temperature at a soldering step provided later. Lens 1 b isshaped in a semi-cylinder as shown in FIG. 14. LED 1 emits light throughlens 1 b following the intensity distribution shown in FIG. 15. When theemitted light is viewed in direction “G” as shown in FIG. 14, the lightis distributed sharply and has a peak just above emitting element 1 bbecause of the curve of lens 1 b as shown in FIG. 15( a). When theemitted light is viewed in direction “H” as shown in FIG. 14, the lightis distributed moderately as shown in FIG. 15( b). When LED 1 thusformed is disposed in the surface lighting device, the light oncehitting surrounding member can be reduced, thereby reducing absorbedloss of light energy due to reflection and absorption of the light. As aresult, the utilization factor of the light is increased.

In the case discussed above, an angle formed by the axial direction ofthe semi-cylinder and X direction shown in FIGS. 1 and 2 preferablyapproximates to 90 degree, so that the better utilization factor of thelight is expected. These two directions preferably forms right angles,because the maximum utilization factor is expected in this case.

In this first embodiment, one LED having one light-emitting-element isdisposed in a surface lighting device. However, if one LED with aplurality of light emitting elements having different light wavelengthsis disposed in the surface lighting device and then each current flowingthrough respective elements is controlled, the device can light not onlyin colors corresponding to a number of elements but also in any halftones.

FIG. 16 is a perspective view of an LED in accordance with the firstembodiment. LED 20 comprises three light emitting elements havingdifferent light wavelengths. Three elements 20 a, 20 b and 20 c aremounted onto substrate 20 d. Element 20 a emits approx. blue color,element 20 b emits approx. green color and element 20 c emits approx.red color.

Substrate 20 d is preferably made from a material of highly insulatedand highly thermal conductive.

Power feeding electrodes 20 f, 20 g and 20 h are formed on substrate 20d so that the electrodes can power elements 20 a, 20 b and 20 c. Acontroller (not shown) is disposed for controlling the powers fed to theelements so that light emitted from light-emitting-elements 20 a, 20 band 20 c can be controlled. As a result, the surface lighting device canproduce any colors.

The electrodes 20 f, 20 g and 20 h are extended to at least one of alateral face or a back face so that they can be terminals for couplingLED 20 when LED 20 is mounted onto a circuit board. The electrodes 20 f,20 g and 20 h can be formed by a thin film or a thick film so that LED20 can be directly mounted onto the surface of the circuit board. As aresult, the productivity is increased.

Lead-wires 20 i are used for coupling the electrodes 20 f, 20 g, 20 hwith the electrodes (not shown) formed on light emitting elements 20 a,20 b, 20 c. A wire-bonding method is used, in general, for thiscoupling.

A transparent member 20 e covering elements 20 a, 20 b, 20 c is disposedon substrate 20 d, and this member 20 e restrains the elements frombeing deteriorated due to exposure to the air. This also prevents thecoupling terminals (e.g. coupled by the wire-bonding) from being cut ordisengaged due to vibrations at an actual use or in manufacturing.

When this single LED having the construction discussed above is used,the surface lighting device can change lighting colors without consumingthe power so much because it does not employ a plurality of LEDs. Thetransparent member 20 e is manufactured in this way: Resin material ispreferably molded by a transfer-molding or an injection molding so thatmore formability and higher accuracy are obtained. The transparentmember 20 e may be made of glass so that changes in materials and shapeof the member with time can be substantially reduced. As a result, aglass-made light-transparent member 20 e increases its reliability.

It is preferable for the transparent member 20 e to have a function ofgathering and scattering the light emitted from light-emitting-elements20 a, 20 b and 20 c, because this function increases the lightutilization factor. The structure of the transparent member 20 e allowslight to spread widely toward an area to be subjected to widerirradiation, and to narrow toward an area to be subjected to narrowerirradiation, so that this structure can guide the light in a thinsurface-lighting-device, among others, with high efficiency.

The chromaticity of light emitted from element 20 a resides near thecoordinates (x, y) (0.1, 0.04), that of element 20 b resides near thecoordinates (x, y)=(0.12, 0.76) and that of element 20 c resides nearthe coordinates (x, y)=(0.72, 0.27) in CIExy color atlas. Therefore,controlling the respective currents of those elements makes the LED emitthe color represented by “Q” section in CIExy color atlas shown in FIG.17.

In FIG. 16, light-emitting-elements 20 a, 20 b and 20 c included in LED20 are roughly in the same shape. However, when each element is in adifferent shape or a dimensional center of the element is different froma light-emitting center, the elements are preferably arrayed so that theline connecting the light-emitting centers is approximately aligned withthe longitudinal direction of the transparent member 20 e. Thisarrangement allows respective lights from the elements 20 a, 20 b and 20c to be used approximately at the same utilization factor. This permitsa user to have the flexibility of controlling light amount and colors.Further, the incident condition of the light from respective elements tolight-guide-board 2 (described later) can be equal. As a result,disperses of incident-light amounts and incident-light axes amongrespective elements are minimized so that sufficient light and excellentcolor tones are obtainable in the surface lighting device.

Respective spaces between light-emitting-elements 20 a, 20 b and 20 care preferably as small as ranging from 0.3 to 1.0 mm therebyrestraining unevenness in luminance and colors. If the space is lessthan 0.3 mm, it is too narrow for wire bonding, resulting in increasinga frequent occurrence of the short circuiting between respectiveterminals. This narrow space would result in a lower yield rate. On thecontrary, if the space is wider than 1.0 mm, it is difficult to restrainthe unevenness in luminance and colors due to different emittingpositions of each element. More preferably, the space ranges 0.4–0.8 mm.With this space, thermal affect to the adjacent elements is minimized,and yet, unevenness in luminance and colors is restrained.

As such, two or more than two light-emitting-elements are employed inLED 20 of the surface lighting device, then a user can select or make acontroller select element(s) to be emitted, e.g. change a lightwavelength or vary a light amount of respective elements, therebychanging emitting colors of the surface lighting device. One of theplurality of elements can be kept for just in case of a element failure.

The plurality of light-emitting-elements disposed in LED 20 havedifferent light wavelengths independently, and at least two elementsemit simultaneously so that LED 20 can emit a different color from whateach light wavelength of the elements originally disposed cannotexpress. In this case, uneven luminance due to different lightwavelengths is minimized because of the narrow space between theelements, and a uniformed mix-color is obtainable. As a result, asurface lighting device free from uneven colors is achievable. This isan advantage over the case when a plurality of light sources havingdifferent light wavelengths are disposed with wider spaces in betweenand these light sources emit simultaneously.

In the description hereinafter, LED 1 can be replaced with LED 20 unlessotherwise specified.

In FIG. 1, light-guide-board 2 made of transparent material guides thelight from LED 1 and emits the light to outside from a given place. Thematerial of board 2 is preferably highly transparent resin such asmethacrylic resin, polycarbonate resin or the like. More specifically,transmittance per one (1) mm thickness is preferably not less than 95%.In the case of a resin board having a length not less than 30 mm, amaterial of which transmittance is not less than 98% is preferably usedso that loss of light amount is minimized and thus greater luminance isobtainable. Resin or glass satisfies these conditions, and the resin, inparticular, has more formability by an injection molding and is betterfor mass production. In this embodiment, methacrylic resin featuring ahigh light-transmittance is thus used. A refractive index of light guideboard 2 is preferably not less than 1.3, and more preferably not lessthan 1.4. This condition allows the guided light to reflect totally withease at an interface with an air layer (refractive index is approx. one(1)) so that light amount leaked out of light-guide board 2 can berestrained. As a result, loss of the light incident on light-guide-board2 caused by emitting the light to outside can be minimized, and thelight utilization factor is increased thereby lowering the powerconsumption of the surface lighting device.

Light guiding section 3 of light-guide-board 2 spreads the light emittedfrom LED 1 in the width direction of board 2 through incident plane 3 aand reflecting plane 3 b. The length of light-guiding-section 3 ispreferably as short as possible because this short length allows thesurface lighting device and an apparatus employing this device to besmall in dimensions. More specifically, the length of not more than 8 mmis demanded by the market.

The light from LED 1 approaches incident plane 3 a before the lightreaches light-guiding-section 3. Incident plane 3 a is not perpendicularto upper face 2 a of light-guide-board 2. This structure restrainseffectively the light of LED 1 from being transmitted across thetransparent board of light-guiding-section 3, and thus guides more lightto light-guide-board 2.

Reflecting plane 3 b (a lateral face of board 2) reflects most of theincident light first of all. Plane 3 b is slanted with respect tolateral face 2 b of board 2. Slant angle θ (when the slope is formedwith a curve, an angle of a slant connecting both the ends) may be wideenough, more specifically, the angle ranging between 90° and 135° allowsthe light to approach entire board 2 even board 2 has a wide width.Lately, in a portable terminal apparatus, a display section becomeswider, yet an apparatus per se becomes smaller. Therefore, slant angle θis more preferably not less than 65° so that light-guiding-section 3 canbe shorter yet light emitting section 4 can be larger. An angle formedby crossing reflecting planes 3 b, i.e. an opening angle oflight-guiding-section 3, is preferably not less than 90°, and morepreferably not less than 130°. This structure allows the length ofsection 3 to be not more than 8 mm even if light emitting section 4 hasa width (W2) of 16 mm. In other words, the length oflight-guiding-section 3 can be reduced and yet the width oflight-emitting-section 4 can be increased.

The shape of reflecting plane 3 b may be flat or curve, depending on theluminance distribution of LED 1 and a shape of light-guide-board 2, andthe shape of plane 3 b is determined so that an optimum luminancedistribution can be obtained on light-guide-board 2. Disposingreflecting plane 3 b uniforms the distribution of the incident light onlight emitting section 4 even if the length of light-guiding-section 3is shortened. As a result, a surface lighting device having littleunevenness in luminance and high visibility is achievable.

When LED 20 replaces LED 1, light-emitting-elements 20 a, 20 b and 20 cincluded in LED 20 are aligned on a line, i.e. an axial line, positionedapprox. equidistantly between two incident planes 3 a as shown in FIG.21. This structure restrains an inconvenience of each element emittingdifferent amounts of light incident on light-guiding-section 3, anduniforms the luminance distribution. As a result, a surface lightingdevice having high visibility and little unevenness in luminance isachievable.

This axial line is defined as a straight line connecting the mostintensified points in the intensity distribution of LED light, or anapproximating line of the same. If the light-intensity-distribution isdifferent from Gauss distribution, and the light intensity isdistributed diversely, the axis line is defined as a line vertical toemitting surfaces of the elements. Further, if the vertical line doesnot run through the emitting surfaces, the vertical line can be modifiedto run through the emitting surfaces. These definitions are applicableto the “axis line” hereinafter.

In FIG. 1, light-emitting-section 4 situated on light-guide-board 2emits the light incident on board 2. When an average surface roughnessof light-emitting-section 4 is not more than 1 μm, the light emitted isscarcely disturbed on an interface between emitting section 4 and air. Asurface lighting device with high visibility is thus achievable.

In FIG. 2, scattering section 5 is formed on lower face 2 c oflight-guide-board 2, and reflects or transparently transmits theincident light in diverse directions. Scattering dots 5 a are formed sothat the dot area becomes greater at a longer distance from LED 1, andare formed with an ink ranging from milky-white to white. Dots 5 ascatter the light incident thereon. In most cases, dots 5 a are printed.Screen printing and pad printing among others are preferable becausethese methods can increase the productivity of manufacturing. Padprinting, in particular, can print scattering dots 5 a uniformly even ifthe surface of light-guide-board is not flat.

Scattering dots 5 a as structured above can produce excellent scatteringof light and minimize light absorption into the dots. The distributionof the printed area of scattering dots 5 a can be changed depending onthe location, so that uniform luminance distribution oflight-emitting-section 4 is achievable. The ink for the dots preferablyemploys transparent binder and white particles such as titanium oxidedispersed therein. Besides the white particles, glass beads having arefractive index greater than the binder or air bubbles can be mixed inthe ink with the same effect.

Numbers of fine peaks or valleys formed directly on scattering section 5by molding can function as scattering light, thereby replacingscattering dots 5 a.

Reflecting layer 6 is placed beneath the lower face of scatteringsection 5 and has a high reflective rate. Reflecting layer 6 reflectsparts of outgoing light transmitted through scattering section 5 andthen emitted from light-guide-board 2, so that the light reflectedreturns inside the board 2 again. Reflective layer 6 is made ofpolyethylene tere-phtalate (PET) sheet or the like. A metalvacuum-deposited sheet or a foamed-sheet increases a reflection.

Reflecting layer 6 may be provided independently in a form of a separatemember, or formed directly on light-guide-board 2 by printing or vacuumdeposition in advance. This direct forming can simplify themanufacturing processes of the surface lighting devices, therebyincreasing the productivity and lowering the manufacturing cost. A thintype surface lighting device is thus achievable.

When reflecting layer 6 is directly formed on light-guide-board 2, layer6 may be formed only on scattering dots 5 a and not formed in otherarea. This structure allows the light passing through dots 5 a toreflect on layer 6 and other light to reflect totally insidelight-guide-board 2. Thus the light is reliably guided tolight-emitting-section 4.

When reflecting layer 6 is independently provided in a form of adifferent member, an air layer is provided between layer 6 and board 2so that both of total internal reflection light of board 2 andreflection light on layer 6 can be utilized. As a result, a utilizationfactor of the light is increased. Layer 6 can be bonded to board 2 inparts following the given positional relation, thereby simplifying theassembly processes of the surface lighting device.

Reflecting layer 6 may be coupled to second recess 8 c of holder 8(detailed later) in advance. This structure eliminates an inconvenienceat assembly of the surface lighting device. The inconvenience is this:Board 2 and layer 6 would be bonded with some slippage, which preventssecond recess 8 c from accommodating layer 6. As a result, thisstructure increases an yield rate of the surface lighting device.

A surface of holder 8 can replace reflecting layer 6, and reflects thelight. This structure eliminates layer 6.

Scattering layer 7 is disposed on the upper face oflight-emitting-section 4. When the light passes through layer 7, layer 7scatters the light in diverse directions. Scattering layer 7 is made oftextured PET sheet, but not limited to this material only. Layer 7 maybe provided independently in a form of a separate member, or formeddirectly on light-guide-board 2 by printing or molding. This directforming method can simplify the manufacturing processes of the surfacelighting device thereby reducing a number of components. This structureincreases the productivity and lowers the manufacturing cost of thesurface lighting device, further, realizes a thin type surface lightingdevice.

When layer 7 is independently provided in a form of a separate material,total reflection on upper face 2 a of board 2 allows the light to beguided to the inside of entire board 2, thereby reducing unbalance oflight amount. In this case, layer 7 may be bonded to board 2 in advancefollowing the given positional relation. This simplifies the assemblyprocesses of the surface lighting device.

Holder 8 accommodates light-guide-board 2, reflecting layer 6 andscattering layer 7 at desired places. Holder 8 is made of one of variousmetals such as stainless steel, iron, or aluminum, or resin. Resin ispreferable among other because of excellent formability, massproductivity and lightweight. Acrylonitrile-butadiene-styrene (ABS)resin, or poly-carbonate resin is a preferable material for holder 8. Acolor of these materials has preferably a high reflection factor such aswhite in order to return the light running out of board 2 from partsother than light-emitting-section 4 into board 2 again efficiently. Whenthe material having a reflection factor of not less than 80% withrespect to the wavelength of LED's emitting light is used, the lightutilization factor is increased. As a result, necessary luminance isobtainable with less power. In this embodiment, the light from lateralface 2 b of board 2 reflects on the inner face of holder 8. However,another reflecting plane can be provided onto this inner face. Thisreflecting plane is made of metal or dielectric material having a higherreflectance.

Holder 8 accommodates light-guide-board 2, reflecting layer 6 andscattering layer 7 at desired places. This accommodating function isdetailed hereinafter.

In holder 8, first recess 8 a, barrier plate 8 b, second recess 8 c, rib8 d, room 8 e, barrier plate 8 g and space 8 i are formed.

First recess 8 a accommodates light-guide-board 2. At least one part ofthe outer circumference of recess 8 a engages with the outer wall ofboard 2, and functions as a position regulator for board 2 with respectto holder 8. A depth “h” of recess 8 a is preferably greater than thethickness of board 2. This structure allows the light leaked from alateral face of board 2 to reflect on a side face of recess 8 a and thenreturn to board 2 again. The light utilization factor is thus increased,and this increases the luminance of the surface lighting device.

Second recess 8 c accommodates reflecting layer 6, and is formed byfurther depressing a part of bottom face of first recess 8 a. The depthof second recess 8 c is greater than the thickness of layer 6.

Barrier plate 8 b is disposed between room 8 e and first recess 8 a in athickness direction of board 2. Barrier plate 8 b prevents most of thelight from LED 1 from entering into board 2 directly, in particular, tothe board center and its neighbor adjacent to LED 1. Barrier plate 8restrains a light-emitting-section (section C) near to LED 1 fromilluminating outstandingly comparing with other areas. This structureallows the surface lighting device to distribute luminance more evenlyand effect better visibility. Plate 8 b is preferably unitarily moldedwith holder 8, and this increases the mass-productivity. This unitarymolding can eliminate a step of aligning the light from LED 1 with plate8 b, a step of aligning plate 8 b and holder 8 and a step of bonding. Asa result, the productivity of manufacturing the surface lighting deviceis increased, and its yield rate is improved. In this embodiment,barrier plate 8 b is made to be a shielding plate; however, it is notnecessary to use a perfect shielding plate, and the shielding plate maybe slit or perforated. Plate 8 b is not always unitarily molded withholder 8.

Barrier plate 8 g is disposed approx. in parallel with inner surface ofboard 2 from the top of panel 8 b on the emitting side of emittingsection 4 to the top of rib 8 d on the same side. Panel 8 g reflects thelight emitted from LED 1 and discharged upwardly and enters the lightinto board 2 finally. In this embodiment, plates 8 g, 8 b and holder 8are unitarily molded.

Barrier plate 8 g efficiently guides the light emitted upward of LED 1into guide board 2, and discharges this upward light directly outsidethe surface lighting device. This structure prevents the light fromleaking out of sections otherwise not to illuminate.

The width of plate 8 g (shown in FIG. 2) approx. equals the distancebetween two incident planes 3 a (shown in FIG. 1) so that gap 10 betweenplate 8 g and board 2 can be almost eliminated. As a result, leakagelight from this gap is minimized.

Respective inner faces of plates 8 b and 8 g are flat with respect toLED 1 in this embodiment; however, if the inner faces are protrudedtoward LED 1, these inner faces reflect the light from LED 1 in widerreflection angles, so that the light is guided efficiently into board 2.

Ribs 8 d reinforce holder 8 and increase the mechanical strength ofholder 8. Further, rib 8 d reflects at least parts of scattering lightfrom LED 1 on its side face so that it can guide a part of light (notguided directly into light-guiding-section 3) into guiding section 3indirectly. This structure increases the utilization factor of the lightemitted from LED 1, thereby realizing a surface lighting device withsufficient luminance with less power.

In room 8 e where the light emitted from LED 1 travels before the lightreaches incident plane 3 a, the light is scattered by dust and the like,so that the light amount guided to light-guiding-section 3 is reduced.Ribs 8 d preferably have approx. the same height so that end faces 8 fthereof can closely fit a substrate (not shown) to be disposed underribs 8 d. This structure reduces amount of dust invading into room 8 eso that the light amount scattered by the dust and not entering inguiding section 3 can be reduced. As a result, the light utilizationfactor is increased.

Space 8 i prevents components mounted on the circuit board (not shown)from touching the surface lighting device. Space 8 i allows the circuitboard to widen components-mountable areas.

This structure, i.e. holder 8 accommodating light-guide-board 2,reflecting layer 6 and the like, allows the surface lighting device tobe thinner, which meets users' request.

Several methods of assembling board 2, layers 6 and 7 into holder 8 areavailable as follows:

-   -   (a) Bond board 2, layers 6 and 7 at a given positional relation,        then incorporate this sub-assembly into holder 8.    -   (b) Form reflecting layer 6 and scattering layer 7 on the        surface of board 2 by printing or vacuum deposition, then        incorporate board 2 into holder 8.    -   (c) Accommodate separate layer 6 into second recess 8 c of        holder 8, then incorporate board 2 on which layer 7 has been        bonded or formed into holder 8.    -   (d) Accommodate layer 6 into second recess 8 c of holder 8, then        incorporate board 2 into first recess 8 a, and finally, bond        layer 7 onto a given position on board 2.

According to method (a), two processes, i.e. one is assembly of board 2,layers 6 and 7, the other is assembly of a surface lighting device, canbe carried out parallel before holder 8 is incorporated. This simplifiesthe total assembly of the surface lighting device and increases themanufacturing productivity.

According to method (b), a number of components can be reducedefficiently, and thus a number of steps or assembly lines can bereduced. The manufacturing productivity is thus further improved.

According to method (c), layer 6 is situated in second recess 8 creliably, so that defectives due to the slippage between layer 6 andrecess 8 c can be restrained. The yield rate of the surface lightingdevices is thus improved.

An operation of the surface lighting device in accordance with thisembodiment is demonstrated hereinafter.

Some light out of the light emitted from LED 1 reaches barrier plate 8 bof holder 8. Being blocked by barrier plate 8, this light is not inputdirectly to the light-guiding-section 3 but is reflected on plate 8 b.Other light arriving at barrier plate 8 g is blocked by plate 8 g, andis not emitted directly outside the device but reflected on plate 8 g. Apart of the light reflected on plates 8 b and 8 g approaches incidentplate 3 a and enters into light-guiding-section 3, and then this lightis reflected on reflecting plate 3 b before entering light-guide-board2. This incident light is emitted directly from light-emitting-section 4or indirectly through scattering section 5 and reflecting layer 6.

On the other hand, some other light emitted from LED 1 not strikingplates 8 b and 8 g mostly enters into board 2 through incident plate 3a. This incident light travels through guiding section 3 and strikesreflecting plate 3 b, which reflects this light tolight-emitting-section 4 and scattering section 5. Parts of this lightis irradiated from section 4, and other part of this light is reflectedirregularly on scattering dots 5 a then irradiated from emitting section4. Another part of this light travels through scattering section 5. Thenreflecting layer 6 reflects and returns the light into board 2 again,and finally, the light is irradiated from emitting section 4.

The light irradiated from light-emitting-section 4 travels in scatteringlayer 7 and scatters in diverse direction. Without scattering layer 7, apattern of dots 5 a would be distinctly recognizable by human eyes;however, disposing dots 5 a veils the dot pattern not recognizably.

As discussed above, providing barrier plate 8 b changes the distributionof light emitted from LED 1, so that the luminance at section C near LED1 is prevented from increasing outstandingly. As a result, uniformluminance is obtained.

Several samples of surface lighting device are produced for evaluatingthe visibility in order to realize a small surface lighting devicefeaturing high visibility, i.e. few recognition errors. Variousconditions are applied to these samples. Each sample comprises onesingle LED and a short length of light-guiding-section 3 yet producingan excellent luminance distribution.

In the first sample, the following conditions are evaluated:

1. An area of light-emitting-section 4 per LED is not less than 500 mm²,and a distance between LED 1 and section 4 is not more than 8 mm.Further, a ratio of maximum luminance vs. minimum luminance at section 4is not less than 0.3. When these conditions are satisfied, the surfacelighting device, in general, provides a clear display with excellentvisibility.2. In addition to the above conditions, when the above ratio is furtherfocused to not less than 0.4, the device can provide a clear displayfree from uneven luminance. As a result, the ratio should be set at notless than 0.3 and preferably not less than 0.4, so that the surfacelighting device can provide efficiently a clear display free fromproblems of LCD visibility.

In the second sample, a relation between an average luminance ofemitting-section 4 and visibility is evaluated with the followingconditions:

Light emitting area per LED is not less than 500 mm², and the distancefrom LED 1 to light-emitting-section 4 is not more than 8 mm. In thesecond sample satisfying the condition discussed above, an averageluminance of emitting section 4 is varied. The result is this: When theaverage luminance is less than 1 cd/m², the device provides asignificantly dark display. In the case of not less than 1 cd/m², thedevice provides a display that users can recognize the content of thedisplay even in a dark place. When the average luminance is raised tonot less than 3 cd/m², the device can provide a clear and easy-to-seedisplay. However, when it exceeds 200 cd/m², the device makes a displaytoo much bright and not easy-to-see. Therefore, the average luminance oflight-emitting-section 4 desirably ranges between 1 cd/m² and 200 cd/m²so that the surface lighting device can provide an LCD at ambientcondition for human eyes.

In the third sample, a relation between a change rate in luminance andrecognizable uneven luminance is evaluated with the followingconditions:

Light emitting area per LED is not less than 500 mm², and the distancefrom LED 1 to light-emitting-section 4 is not more than 8 mm. In thethird sample satisfying the condition discussed above, a rate ofluminance change is varied. The result is this: When a luminance changeper unit length is at any value not more than the value of (averageluminance)×100 cd/m³, the sample produces a little uneven luminance.Further, at any value not more than the value of (average luminance)×80cd/m³, the sample scarcely produces uneven luminance. Therefore, aluminance change per unit length is desirably at any value not more thanthe value of (average luminance)×100 cd/m³, and more preferably, thechange is at any value not more than the value of (average luminance)×80cd/m³. This adjustment allows the surface lighting device to beefficient and free from recognizable uneven luminance, thereby realizinga clear and easy-to-see surface lighting device.

In the fourth sample, a relation between a half width of the lightwavelength of the LED and clearness of the display is evaluated with thefollowing conditions:

Light emitting area per LED is not less than 500 mm², and the distancefrom LED 1 to light-emitting-section 4 is not more than 8 mm. In thefourth sample satisfying the condition discussed above, a half width ofthe light wavelength of LED 1 is varied. The result is this: When thehalf width is not less than 50 nano-meter, the sample makes a displaynot clear and vague. When the half width is not more than 50 nano-meter,the sample makes the display rather clear and recognizable. When thehalf width is further shortened down to not more than 40 nano-meter, thesample makes the display clear and crisp for human eyes. If a portableterminal employs such a surface lighting device, users can see clear andcrisp display and catch information exactly.

In the fifth sample, emitting efficiency of the LED on the main opticalaxis is evaluated with the following conditions:

Light emitting area per LED is not less than 500 mm², and the distancefrom LED 1 to light-emitting-section 4 is not more than 8 mm. In thefifth sample satisfying the condition discussed above, emittingefficiency of the LED on the optical axis is evaluated with respect toan easy-to-see display. When emitting efficiency is not less than 1.0cd/A, the sample can realize the average luminance of 1 cd/m². Thiscontributes substantially to power saving of the portable apparatus.

The factors obtained from the five evaluations discussed above arecombined, and a surface lighting device satisfying these combinedfactors is produced in order to realize less-powered, more easy-to-see,and eye-friendly device.

In the case of using plural LEDs, each LED desirably satisfies thosefive factors so that a surface lighting device can produce aneasy-to-see and eye-friendly display with less power upon lighting anyLEDs.

Exemplary Embodiment 2

The second exemplary embodiment is demonstrated hereinafter withreference to FIG. 6 and FIG. 7.

FIG. 6 is a perspective view of a holder of a surface lighting device inaccordance of the second embodiment of the present invention. FIG. 7 isa cross sectional view of barrier plate 8 g of the same, taken alongcross section E expressed with broken line in FIG. 6.

In FIG. 7, reflecting plate 8 h is an inner face of barrier plate 8 g onLED 1 side, and formed by approx. V-shaped plate. Reflecting plate 8 hchanges a traveling direction of almost all the light emitted upwardlyfrom LED 1 to the direction of reflecting plate 3 b shown in FIG. 1.Reflecting plate 8 h guides most of the light emitted from LED 1 tolight-guide-board 2, thereby increasing utilization factor of the light.In this case, the light widens its ray-bundle substantially beforeentering into light-emitting-section 4, compared with the case when thelight from LED 1 is directly guided into board 2. Therefore, thisstructure allows the distribution of light incident on emitting section4 to be more even, and minimizes unevenness in luminance of the lightemitted from section 4.

When LED 1 produces symmetrical light-intensity-distribution, a vertexor ridge line of the V-shaped plate of reflecting plate 8 h is arrangedto be on an extended axial line of LED1 so that plate 8 h reflectsapprox. equivalent light-amount on either slope of V-shaped plate. Thisstructure allows light-emitting-section 4 to reduce the luminancedistribution, and realizes a easy-to-see surface lighting device.

LED 20 shown in FIG. 16 has a plurality of light emitting elements 20 a,20 b and 20 c aligned. In this case, a straight line connectingrespective emitting centers of the elements (hereinafter referred to asLED-center-line) and the ridge line of the V-shaped panel of plate 8 hviewed from top form an angle not more than ±10° or preferably approx.0° so that a better luminance distribution is produced. TheLED-center-line can be an approximate line thereto. When lightwavelength of the light reflected on V-shaped plate 8 h and guided toreflecting plate 3 b loses balance on either side (or upper and lowersides), luminance distribution becomes unfavorable. The structurediscussed above can restrains uneven colors produced by emittingplurality of light-emitting-elements simultaneously. The uneven colors,in this case, show fine differences in colors in every direction.

Respective lengths of axial-lines from elements 20 a, 20 b, 20 c toreflecting panel 8 h are approx. equal so that the light-distributionbecomes more uniform. As a result, a surface lighting device featuringless unevenness in both luminance and colors as well as high visibilityis achievable.

Meanwhile, a display unit utilizing the unbalance of light wavelengths(e.g. a rainbow colored display unit) does not need the structurediscussed above.

When LED 1 produces an asymmetric light-intensity distribution, theareas of V-shaped plates forming reflecting plate 8 h are variedcorresponding to the asymmetric distribution so that the reflected lightamounts on both sides can be approx. equal. As a result, a surfacelighting device featuring a small luminance distribution at thelight-emitting-section and easy-to-see operation is achievable. Theareas of V-shaped planes can be varied intentionally so that a luminancedistribution at emitting section 4 can be modified.

Incident plane 3 a is preferably slanted toward LED 1 and reflectingplane 8 h so that the light directly entering into light-guiding-section3 and the light entering via plane 8 h (both the lights emit from LED 1)are efficiently entered into light-guide-board 2.

The angle formed by the V-shaped planes is determined based on thefollowing factors so that the light utilization factor can be increased:(1) the distance between LED 1 and plane 8 h, (2) the distance betweenplane 8 h and incident plane 3 a and (3) the thickness of board 2.

Other parts have approx. the same constructions as described in thefirst embodiment.

In this second embodiment, approx. V-shaped reflecting plane 8 h isformed on barrier plate 8 g; however, the same V-shaped reflecting planemay be formed also on the inner face of barrier plate 8 d on LED 1 side.This further increases the light amount entering into board 2. A crosssection of plane 8 h can be U-shaped or any other shapes which maximizesthe light amount entering incident plane 3 a.

An operation of the surface lighting device discussed above isdemonstrated hereinafter. The light emitted from LED 1 toward barrierplate 8 g (in direction Z shown in FIG. 7) rarely arrives directly atguiding section 3, but most of the light arrives at reflecting plane 8h. Most of the light reflected and changed in travelling direction fromZ to Y (shown in FIG. 7) by plane 8 h enters incident plane 3 a. On theother hand, parts of the light emitted from LED 1 enters directly intolight-guide-board 2 through incident plate 3 a. As such, the lightincident on board 2 is reflected on plane 3 b in the directionrepresented by X shown in FIG. 1, then emitted fromlight-emitting-section 4.

In the second embodiment as discussed above, reflecting plane 8 h formedby approx. V-shaped plates is provided, thereby reflecting and expandingthe light emitted in direction Z in direction Y. Then the light travelsin direction X. This structure guides efficiently the light emittedupwardly (toward barrier plate 8 g) from LED 1 to light-guiding-section3. This upward light has been rarely utilized in the first embodiment.This structure thus substantially increases the light utilizationfactor, and realizes an efficient surface lighting device with lesspower consumption. In addition, this structure allows the light incidenton light-emitting-section 4 to be more uniform, so that a highly visiblesurface-lighting-device with less uneven luminance is achievable. In themost cases of this structure, the light emitted from LED 1 or LED 20travels along X, Y, Z axes.

Reflecting plane 8 h can be structured as shown in FIG. 8, which is across section of neighbors of barrier plate 8 g in accordance with thesecond embodiment. In FIG. 8, reflecting plane 8 h is recessed intoconcave. This concave face not only reflects the light scattered fromLED 1 but also narrows the scattering angle. Reflecting plate 8 h thusconverges the incident light and changes a travelling direction. Thisconcave reflecting plate 8 h further efficiently guides the lightemitted upwardly from LED 1 into light-guiding section 3 than thestructure discussed previously in this embodiment, thereby improving anefficiency of the surface lighting device.

Reflecting plane 8 h can be structured as shown in FIG. 9. FIG. 9 is across section of neighbors of another barrier plate 8 g in accordancewith this embodiment. The surrounding area of vertex or ridge line ofreflecting plane 8 h shown in FIGS. 7 and 8 forms a sharp acute angle,so that the area is fragile by being hit with other members. The areajust above LED 1 illuminates outstandingly than other areas. This wouldcause a large difference in light amount striking the two slopes ofreflecting plate 8 h if the relative positional relation between LED 1and plate 8 h is deviated due to manufacturing disperse of the surfacelighting devices. This difference in light amount produces unevenluminance at light-emitting-section 4. Reflecting plate 8 h shown inFIG. 9, on the other hand, a sharp section is cut away and“would-be-vertex” or “would-be-ridge-line” of V-shaped plate is nowround form. This structure prevents the light just above LED 1 fromstriking directly the slopes of plate 8 h. As a result, this structureindeed lowers the light utilization factor a little, but minimizesuneven luminance at light-emitting section 4.

Exemplary Embodiment 3

The third exemplary embodiment of the present invention is demonstratedhereinafter with reference to FIG. 10, which is a plan view of a surfacelighting device in accordance with the third embodiment. As shown inFIG. 10, reflecting plate 3 b forms convex, and fitting sections ofholder 8 also form concave faces in order to fit form of plate 3 b. Inthis structure, the light emitted from LED 1 approaches incident plane 3a and enters into light-guide-board 2 directly, or indirectly viabarrier plate 8 b and reflecting plane 8 h. The incident light travelsthrough light-guiding-section 3 and strikes reflecting plane 3 b. Convexreflecting plane 3 b scatters the light inside of guiding section 3, andthe light travels to scattering section 5 by being reflected andscattered with the inner face of holder 8. Convex reflecting plane 3 bscatters the light, thereby uniforms luminance at light-emitting section4. The curvature of reflecting plane 3 b is preferably changedresponding to an intensity-distribution of the light emitted from LED 1and entering to plane 3 b. In other words, the curvature decreases at astronger intensity thereby scattering the light in a wider angle, andthe curvature increases at a weaker intensity thereby restraining thelight from scattering. This structure is obtainable with ease bydesigning the mold. This third embodiment can uniform the luminance.

Exemplary Embodiment 4

FIG. 18 is a front view of a surface lighting device in accordance withthe fourth exemplary embodiment. FIG. 19 is a cross section of the samedevice taken along line 100—100 of FIG. 18. FIG. 20 is a front view of alight-guide-board used in this embodiment.

In FIG. 18, the surface lighting device comprises LED 41 andlight-guide-board 42. Board 42 includes light-inlet 50, light-guidingsection 43 and light-emitting section 44. LED 41 is approx. the same asLED 1 or LED 21 discussed in previous embodiments.

In FIG. 20, dotted line defines a border between light-guiding section43 and light-emitting section 44. Given corners and ends of light-guideboard 42 are expressed with “m”, “q”, “p” and “l”. Light inlet 50includes incident plane 50 a which introduces the light from LED 41 intoboard 42, and reflecting plane 50 b in FIG. 19 which reflects the lightfrom incident plane 50 a toward light-emitting section 44. Light inlet50 widens from ends “q” and “m” of Board 42 toward corners “p” and “l”and forms V-shape. Light-emitting section 44 emits the light incident onupper face of board 42. Scattering dots 45 a increases their areas at agreater distance from LED 41 as shown in FIG. 20.

In FIG. 19, scattering section 45 is formed beneath the lower face ofboard 42. Reflecting layer 46 is made of highly reflective material andis disposed beneath scattering layer 45. Reflecting layer 46 returns thelight traveling through scattering section 45 and running out of board42 to board 42 again.

Scattering layer 47 is disposed on light-emitting section 44. Holder 48accommodates board 42, reflecting layer 46 and scattering layer 47 atdesirable places. The functions of respective sections and the methodsof forming them are the same as discussed in the first embodiment.

An operation of the surface lighting device as structured above isdemonstrated hereinafter. First, the light from LED 41 enters toincident plane 50 a. Then the light is reflected on reflecting plane 50b, and most of the light has an angle component satisfying conditions oftotal reflection at an interface between board 42 and air, so that thislight is guided inside the board 42. Parts of the light incident onboard 42 is reflected on light-guiding section 43, then guided towardlight-emitting section 44. A part of the light is directly guided tosection 44. In light-emitting section 44, the light guided byguiding-section 43 is totally reflected and shielded efficiently;however, the light striking scattering dots 45 a on the lower face ofsection 44 is reflected in diverse directions or travels through. Onlythe light having an angle smaller than the critical angle at the totalreflection runs out of board 42. Some light out of this light arrives atemitting section 44, and then is emitted. Some other light strikesreflecting layer 46 and holder 48, and then is reflected and returnedinside board 42 again. As such, almost all the light, except some amountabsorbed on the way, guided inside board 42 is emitted from section 44for surface lighting.

In this structure, LED 41 is disposed at the corner of board 42 so thatonly the high intensity light out of the light from LED 41 can be guidedto board 42. This structure thus scarcely produces dark portions whichhave been seen sometimes in a conventional devices, and uniforms theemitting characteristics. Further, this structure allows the distancebetween LED 41 and board 42 to be shorter, and this contributes todownsizing of the surface lighting device.

In the case of LED 41 replacing LED 20 having a plurality of lightemitting elements, the placement of LED 41 is demonstrated withreference to FIG. 22 and FIG. 23. FIG. 22 shows the placement of the LEDhaving a plurality of light emitting elements discussed in the firstembodiment and the light guide board. FIG. 23 is a cross section ofneighbors of the LED, in accordance with this third embodiment, takenalong line 200—200 of FIG. 22.

In FIG. 22, LED 41 is placed so that an angle formed by an emittingcenter line of LED 41 a, 41 b and 41 c and a diagonal line 200—200 ofboard 42 approximates to 90° or preferably almost 90°. The line 200—200runs in the most longitudinal direction viewed from the LED. Thisstructure allows the lengths of axial lines from respective LEDs 41 a,41 b and 41 c to light-inlet 50, incident plane 50 a or reflecting plane50 b to approx. equal with each other. Thus the incident conditions fromrespective elements 41 a, 41 b and 41 c become uniform.

When the emitting center line makes right angles with the diagonal line,uneven luminance can be restrained most efficiently. When an emittingface of the surface lighting device forms a quadrilateral having longersides and shorter sides, such as a rectangle, the emitting center lineforms a wider angle with the longer side direction of the rectangularthan the angle formed with the shorter side direction, so that theadvantages discussed above are obtainable. When light-emitting-section44 forms a shape in which it is difficult to define a diagonal line,longer side or shorter side, LED 41 is placed as follows so that theadvantages discussed above are obtainable: (1) a straight line betweenthe farthest emitting face 44 from LED 41 and an emitting point of LED41 (or an emitting center) forms right angles with the emitting centerline of LED 41, or (2) a straight line forming approx. right angles withthe emitting center line of LED 41 splits light-emitting-face 44 intoapprox. two equal parts.

In this fourth embodiment, the emitting center line forms approx. rightangles with the diagonal line so that respective axial lines fromelements 41 a, 41 b and 41 c in LED 41 to reflecting plane 50 b have thesame length. However, for instance, the heights of elements 41 a, 41 band 41 c are varied (e.g. they form steps, they are disposed on a slope,or they have different heights per se). Then respective emitted lightsenter reflecting plane 50 b. The incident angles or the length of axiallines equal with each other, so that the same advantages are expected.This structure has less restrictions on the relative placement of LED 41and light-guide-board 42 than other structures and produces moredesigning flexibility.

Exemplary Embodiment 5

The surface lighting devices described in the previous embodiments areemployed in various electronic apparatuses, and the devices are used innumbers of portable terminals. In this embodiment, a portable terminalusing the surface lighting devices is demonstrated.

FIG. 11 and FIG. 12 are a plan view and a block diagram of a portableterminal in accordance with the fifth exemplary embodiment. FIG. 13 is apartial cross section of the portable terminal, taken along line 300—300of FIG. 11. In FIG. 11 through FIG. 13, the portable terminal comprisesthe following elements: microphone 29 for transforming sounds to audiosignals;

-   -   speaker 30 for transforming audio signals to sounds;    -   operating unit 31 including push buttons;    -   display 32;    -   antenna 33;    -   transmitting unit 34;    -   receiving unit 35; and    -   controller 36 for controlling speaker 30, transmitter 34,        receiver 35, operating unit 31 and display 32.

Display 32 comprises LCD for displaying text data such as a telephonenumber, and a caller's name based on arrived and transmitted informationas well as searched data. Behind these displayed data, the surfacelighting device is mounted.

An operation of this portable terminal is demonstrated hereinafter.

When the portable terminal receives an incoming signal, receiving unit35 sends an incoming signal to controller 36. Based on the incomingsignal, controller 36 then lights surface lighting device 13 anddisplays a given text data. Further, when a button on operating section31 is pushed to inform the arrival of incoming signal, the signal issent to controller 36. Controller 36 then puts respective sections in areceiving mode. In actual, a signal received by antenna 33 istransformed into an audio signal at receiver 35. The audio signal isoutput from speaker 30 as sound. On the other hand, sound fed intomicrophone 29 is transformed to an audio signal. The audio signal issent out from antenna 33 via transmitting unit 34.

When a user sends an transmitting signal, firstly a signal informing atransmission is sent from operating section 31 to controller 36.Secondly a signal corresponding to a telephone number is sent fromoperating section 31 to controller 36. Then controller 36 transmits thesignal corresponding to the telephone number from antenna 33 viatransmitter 34. The signals fed into controller 36 are often displayedon display 32 by emitting surface lighting device 13. When acommunication with a recipient is established by the transmitted signal,a signal informing a successful communication is sent to controller 36from antenna 36 via receiving unit 35. Then controller 36 putsrespective sections in a transmitting mode. In actual, a signal receivedby antenna 33 is transformed into an audio signal at receiving unit 35.The audio signal is supplied from speaker 30 as sound. On the otherhand, sound fed into microphone 29 is transformed to an audio signal.The audio signal is sent out from antenna 33 via transmitting unit 34.

In this embodiment, sound is transmitted and received. It is not limitedto sound, but text data and the like other than sound can be at leasttransmitted or received by electronic apparatuses with the sameadvantage.

A construction of display 32 and its surrounding is detailed withreference to FIG. 13. Housing 11 includes the following elements:

-   -   LCD element 12 for displaying information of the portable        terminal;    -   surface lighting device 13 used in one of embodiments 1 through        4; and    -   circuit board 14 on which device 13 and electronic circuits are        mounted.

This surface lighting device in the portable terminal allows the displayto reduce uneven luminance. Therefore, a portable terminal with highvisibility and little recognition-errors is achievable. Since only oneLED is used in the device, the portable terminal consumes less power.

When LED 20 including a plurality of light-emitting elements havingdifferent light wavelengths is used in surface lighting device 13, thefollowing advantages are achievable:

-   -   1. An irradiating color is changeable depending on user's taste.    -   2. A time detector is additionally disposed in the terminal, and        a light wavelength to be emitted is switched depending on the        time when the display is irradiated. For instance, a peak of        human luminosity is around 555 nano-meter in light surroundings,        while the peak moves to shorter wavelengths in darker        surroundings. Thus a green element is emitted in the daytime        with the light surroundings, and a blue element is emitted at        night with the dark surroundings to respond to this nature of        human luminosity. This realizes a surface lighting device which        always keeps bright and easy-to-see display. Further, if a        calendar function is incorporated, switching times can be varied        depending seasons so that the LEDs in the device can be switched        at an optimal time around the year. A detector for sensing        outside luminance is disposed, and the colors of LEDs are        changeable responsive an output of the detector.    -   3. A telephone diary has been stored in the terminal, and when        an incoming call arrives, a color irradiated by the surface        lighting device is changeable depending on a caller.

In this fifth embodiment, the surface lighting devices discussed inembodiments 1 through 4 are used; however, other surface lightingdevices discussed previously can be mounted to the terminal with thesame advantages.

Exemplary Embodiment 6

FIG. 24 is a front view of a surface lighting device in accordance withthe sixth exemplary embodiment. FIG. 25 is a cross section of the samedevice, and FIG. 26 is a front view of another surface lighting device.

In FIG. 24, LED 1, LED 20 and the equivalents can replace LED 101.

Light-guide-board 102 is made of an organic material having a hightransparency such as methacrylic resin or polycarbonate resin, or glass.In this embodiment, methcrylic resin featuring a highlight-transmittance is used.

Light-guide-board 102 comprises light-inlet 103, light-guiding section104 and light-emitting section 105. The dotted line connecting corners“r” and “n” of emitting section 105 in FIG. 26 defines an interfacebetween light-guiding section 104 and light-emitting section 105. Givencorners of board 102 are marked with “m”, “q”, “p” and “l”.

Light-inlet 103 guides light inside light-guide-board 102. As shown inFIG. 25, when LED 101 is disposed below light-guide-board 102,light-inlet 103 is formed by an incident plane and a reflecting planewhich reflects incident light to emitting section 105. This reflectingplane is a slope on an end face of board 102 and widens from LED 101 andforms a sector shape. This reflecting plane is disposed just above LED101. This structure allows the light-inlet to scatter the light from LED101, and then the light travels into the light-guide board. As a result,the luminance distribution is improved and the better visibility isexpected. Since LED 101 is placed under light-inlet 103 of board 102,the surface lighting device can be further downsized.

As shown in FIG. 26, light-guiding section 104 widens from ends “q” and“m” of board 2 toward the corresponding corners “p” and “l” and formsV-shape.

Light-emitting section 105 emits the light from light-guide board 102 tothe outside. The construction of section 105 is the same as thatdiscussed in the first embodiment.

The constructions of reflecting layer 109 disposed beneath scatteringsection 106, scattering layer 110 disposed on emitting section 105, andholder 111 are also the same those discussed in the first embodiment.LED 101 is mounted on circuit substrate 112, which holds holder 111 at agiven place in order to position LED 101 so that LED 101 can be placedjust below light-inlet 103.

An operation of the surface lighting device as structured above isdemonstrated hereinafter. First, the light from LED 101 enters toincident plane of light-inlet 103. Then the light is reflected on thereflecting plane, and most of the light has an angle componentsatisfying conditions of total reflection at an interface between resinand air, so that this light is guided inside the board 102. Parts of thelight incident on board 102 is reflected on light-guiding section 104,then guided toward light-emitting section 105. A part of the light isdirectly guided to section 105. In light-emitting section 105, the lightguided by guiding-section 104 is totally reflected and shieldedefficiently; however, the light striking scattering pattern 107 on thelower face of section 105 is reflected randomly in diverse directions ortravels through. Only the light having an angle greater than thecritical angle at the total reflection runs out of board 102. Some lightout of this light arrives at emitting face 108, and then is emitted.Some other light strikes reflecting layer 109 and holder 111, and thenis reflected and returned inside board 102 again. As such, almost allthe light, except some amount absorbed on the way, guided inside board102 is emitted from emitting face 108 for surface lighting.

As such, the light from LED 101 enters to the incident plane oflight-inlet 103, then the reflecting plane reflects this light. Thelight is then guided inside light-guide-board 102. In this case, athicker board 102 allows a distance from LED 101 to light-inlet 103 toincrease, thereby reducing the area of light-guiding section. As aresult, the surface lighting device can be downsized.

In this sixth embodiment, LED 101 is placed at a corner of board 102.The light from LED 101 is guided inside board 102 so that a center axisof light distribution of the incident light can slant with respect tosides 104 a and 104 b of board 102. This structure allowslight-emitting-section 105 to output uniform luminance, therebyrealizing the surface lighting device featuring an excellent visibility.

LED 101 is placed around a corner of light-emitting-section 105 of board102, and light-scattering-regulation angle A1 around light-inlet 103forms an acute angle as shown in FIG. 26. This structure allows somelight out of the light from LED to irradiate section S2 on a scatteringboard shown in FIG. 24. This some light is around point P2 shown in FIG.34 and has a strong relative intensity. Light-inlet 103 is formed with acurved face parallel to light-emitting-section 105, and a cross sectionof the curved face forms an arc. Thus the light around point P1 shown inFIG. 34 having a strong relative intensity can contribute to irradiatingthe section S2. This structure reduces a difference in luminance betweensection S2 and section S1 which is irradiated by the light around pointP1 having a strong relative intensity.

A luminance distribution which does not cause irregular image for humaneyes is desirably not less than 0.3R, where R is luminance rate.R=minimum luminance/maximum luminanceIn order to achieve this condition, the light mainly irradiating sectionS2 has a relative intensity not less than 70%. For this, thelight-scattering-regulation angle A1 is preferably not more than 90degree. In this embodiment, as shown in FIG. 24, the length L1 of alight-guiding-route extending from LED to light-emitting-section isshortened for placing the LED at the corner of the light-guidingsection, and yet, light-scattering regulation angle A1 can be set atless than 90 degree.

Preferable value of angle A1 is 45°≦A1≦90°; and more preferable range is60°≦A1≦85° for further downsizing the surface lighting device. Whenangle A1 is not more than 85°, the light incident on light-guide-board102 is reflected not perpendicularly without fail. Therefore the lightreflected on circumference of light-inlet 103 returns to light-inlet 103without entering into light-emitting-section 105. This structureprevents this reflected light from being stray light, leaking out ofboard 2 and irradiating a wrong place. This structure can guide almostall the light incident on light-guide-board 2 intolight-emitting-section 105, thereby increasing the light utilizationfactor.

In actual, the following two samples are compared under the commoncondition below:

-   -   Condition: light-emitting face is a square with 30 mm sides;        -   light-guiding-route length L1 is 3 mm;        -   thickness of light-guide-board is 1 mm;        -   one green GaN LED is used; and        -   10 mA current flows respective LEDs.    -   Sample 1 to be compared with the sample in accordance with this        embodiment: One LED is disposed at the center,        light-guiding-route length L2 is 3 mm, light scattering        regulation angle A1 is 160 degrees.    -   Sample 2 in accordance with this embodiment: light-scattering        regulation angle A1 is 85 degrees.

Under the conditions discussed above, the luminance distributions ofeach sample are measured: Sample 1 produces luminance rate R=0.18, andsample 2 produces R=0.68. When the sample 2 is viewed through asemi-transparent LCD, almost no luminance distribution is observed. Thiscomparison proves that sample 2 in accordance with this embodiment issubstantially improved.

As such, this sixth embodiment proves that even the light-guiding-routeis shortened, the incident light can be substantially spread in thewidth direction of light-guide-board, so that less numbers of LED candistribute the luminance more uniformly. The shorter length oflight-guiding route allows the light-guide board to be downsized involume, whereby a small size surface lighting device is obtainable. Theless numbers of LEDs can reduce power consumption, and at the same time,reduces a number of processes of mounting LEDs onto a substrate. As aresult, a surface lighting device easy-to-manufacturing and operatingwith less power is achievable.

In this embodiment, straight line 104 b connecting corners “m” and “l”approaches to line 105 (an element of light-emitting section 105) at agreater distance from LED 101. Straight line 104 a connecting corners“q” and “p” also approaches line 105 b (an element of section 105) at agreater distance from LED 101. This structure allows the light emittedfrom LED 101 to travel more efficiently to light-emitting-section 105,thereby distributing the luminance further more uniformly. Section S2,among others, is irradiated efficiently thanks to this structure. Thisstructure also allows a projection area of light-guide-board 102 to besmaller, so that the space within the surface lighting device can bemore efficiently used. As a result, more design flexibility is obtainedand the device can be further downsized.

Next, a display unit employing this surface lighting device and aportable terminal employing the display unit are demonstrated withreference to FIG. 27 and FIG. 28. FIG. 27 is a front view of theportable terminal in accordance with this embodiment, and FIG. 28 is apartial cross sectional view of the same portable terminal. In FIG. 27,the portable terminal is equipped with display section 113 employing LCD117 for displaying a telephone number. FIG. 28 is a perspective view ofdisplay section 113 from the terminal lateral side. LCD 117, comprisingreflection type LCD element 115, is disposed on the surface lightingdevice in accordance with this embodiment, and wiring 116 for display isdisposed to cover LED 101 of the surface lighting device. Employing thesurface lighting device in accordance with this embodiment, LCD 117realizes a small size and a low power consumption free from lowering itsvisibility. If stray light from LED 101 leaks from sections other thanlight-emitting-face 108, wiring 116 for display blocks almost all theleakage light, thereby improving the visibility. A display on LCD 117 ofdisplay section 113 is seen through display-window 118 made oftransparent material. Thanks to employing this LCD 117, a portableterminal operating with a lower power and having excellent visibility isobtainable.

In the portable terminal as structured above, a number of LEDs 101 canbe reduced, so that the terminal consumes less power and LEDs 101 need anarrower space for mounting as well as the light-guiding-sectionrequires a shorter length. As a result, the portable terminal can bedownsized.

The space within the portable terminal can be used more efficiently, sothat more design flexibility is obtainable and the wiring can be donemore efficiently as well as the circuit board can be efficiently placed.This space freedom restrains unreasonable or forcible placement of thecomponents, and this can lower troubles and defectives due tounreasonable or forcible placement of the components. As a result, areliable display unit and a portable terminal are obtainable, and theycan be downsized.

Exemplary Embodiment 7

The seventh exemplary embodiment is demonstrated hereinafter withreference to FIG. 35, which is a front view of a light-guide-board usedin this embodiment. In FIG. 35, light-emitting-section 105 andlight-inlet 103 are the same as those discussed in the sixth embodiment,and the descriptions thereof are thus omitted here.

In this embodiment, end section 104 c of light-guiding section 104 isrecessed toward light-emitting-section 105 from the straight lineconnecting the corners “q” and “p” of light-guide-board 102. End section104 d of section 104 is also recessed toward section 105 from thestraight line connecting the corners “m” and “l”. This structure allowsthe light emitted from LED 101 to spread at angle A4 narrower than angleA3. Therefore, the light nearer to the center, where intensity isstronger, can irradiate section S2 which otherwise receives lowerluminance. As a result, section S2 receives greater luminanceefficiently, and the light-emitting-section produces a narrowerdispersion of luminance distribution.

When an LED having the intensity concentrated at the center as shown inFIG. 34 marked with “II” is employed, this structure allows the light totravel with uniform luminance to light-emitting-section 105. As aresult, the luminance distribution at light-emitting-section 105 can beminimized, thereby realizing a surface lighting device with stableoperation independent of intensity characteristics of LEDs to beemployed.

In this embodiment, end sections 104 c and 104 d are recessed towardsection 105; however, they can be in a wave-like shape, or saw-teethlike shape. This structure can minimize the luminance distribution atlight-emitting-section 105.

Exemplary Embodiment 8

The eighth exemplary embodiment is demonstrated hereinafter withreference to FIG. 30 through FIG. 33. FIG. 30 is a front view of asurface lighting device in accordance with the eight exemplaryembodiment. FIG. 31 is a cross section of the same device taken alongline 400—400 of FIG. 30. FIG. 32 is a front view of a light-guide-boardand a diffused reflection board of the surface lighting device inaccordance with this embodiment. FIG. 33 is a lateral view of an LEDused in this embodiment. Scattering layer 110, holder 111 and circuitsubstrate 112 in FIG. 30 are the same as those described in the sixthembodiment. The descriptions thereof are thus omitted here.

LED 119 comprises light emitting element 123 mounted on substrate 124,and element 123 is covered with transparent and cylindrical resin 125 ofwhich top has recess 126 thereon. An axial line of recess 126 isapproximately parallel to diagonal line 400—400, and thus approximatelyconcave lens is disposed above a light-emitting-face of LED 119. Thisstructure spreads the light from the LED so that a luminancedistribution is improved, thereby increasing the visibility of thedevice. In this embodiment, light-guide-board 120 is constructed withlight-inlet 103 and light-guiding section 104 only, and these twoelements are made of high light-transmitting material such asmethacrylic resin. Lateral sides of board 120 are light-emitting faces120 a and 120 b, and diffused reflection board 121 is disposedadjacently to these light-irradiating faces. Diffused reflection board121 increases its thickness at a greater distance from LED 119, and hasdiffused reflecting pattern 122 thereon. Pattern 122 form numbers ofapprox. triangles in cross sectional view, and the patterns aredistributed in a concentric pattern centered on LED 119 as shown in FIG.32.

In this embodiment, diffused reflection board 121 is made of ABS resinin white color, and unitarily molded with diffused reflection pattern122 by injection molding; however, board 121 can be made of othermaterials than resin as far as the material is in white and has a highreflectance. Pattern 122 can be formed by printing. Board 121 and holder111 can be unitarily molded. The surface lighting device of thisembodiment has less weight than that of the sixth embodiment, thereforea display unit employing this device weighs substantially less, andnaturally, a portable terminal also weighs much less for users to handlethe terminal conveniently.

In this embodiment, the incident light from LED 119 is scattered bylight-guiding-section 104 in the same manner as in the sixth embodiment,and then emitted from light-emitting-faces 120 a and 120 b. The emittedlight is diffusely reflected by diffused-reflection pattern 122 and thenenters into the scattering layer to irradiate the surface. Meanwhile thelight incident on diffused-reflection-board 121 would have moreluminance at a closer distance to LED 119. In order to overcome thisproblem, the pattern 122 is arranged so that the area ratio of thepattern increases at a greater distance from LED 119. This arrangementcontributes to reducing the luminance distribution. The light of LED 119is scattered to some degree by recess 126 in advance and then emitted,therefore, the light at light-guiding-section 104 is progressivelyscattered, thereby further reducing the luminance distribution.

In this embodiment, LED 119 is placed at a corner of light-guiding-board120, and light-scattering regulation angle A2 forms an acute anglearound light-inlet 103 as shown in FIG. 32. This structure improves theluminance distribution for the same reason as described in the sixthembodiment.

In actual, a sample having the following structure measures a luminancedistribution R=0.70, thus an improvement in the luminance distributionis proved: upper surface of diffused reflection board forms a squarehaving sides of 30 mm length, a length of light-guiding-route is 3 mm; athickness of light-guide-board is 1 mm; one green GaN LED is used as alight source; angle A2 forms 85 degree; and current of 10 mA flows theLED.

The eight embodiment as discussed above proves that the small and lightweight surface-lighting-device with low power consumption andeasy-to-manufacture is achievable. The display unit employing thissurface lighting device also becomes small in size and light in weight,consumes less power and provides an excellent visibility. The portableterminal using this display unit can provide the same advantages as thedisplay unit.

Exemplary Embodiment 9

FIG. 36 is a front view of a surface lighting device in accordance withthe ninth exemplary embodiment, and FIG. 37 is a cross section of thesame device. FIG. 38 is a front view of another surface lighting deviceused in this embodiment.

LED 201 in FIG. 36 can be replaced with LED 1 used in the previousembodiments. Light-guide-board 202 comprises light-inlet 203,light-guiding section 204 and light-emitting section 205. Board 2 can bemade of the same material as that of board 2 discussed in previousembodiments. The dotted line connecting corners “r” and “n” of emittingsection 205 defines an interface between light-guiding section 204 andlight-emitting section 205 as shown in FIG. 38. Given corners of board202 are marked with “m”, “q”, “p”, “l” and “o”.

Light-inlet 203 guides the light inside light-guide-board 202. When LED201 is disposed below light-guide-board 202, light-inlet 203 is oftenformed by an incident plane and a reflecting plane which reflectsincident light to emitting section 205. This reflecting plane is a slopeon an end face of board 202 and widens from LED 201 and forms a sectorshape. This reflecting plane is disposed substantially above LED 201.This structure allows the light-inlet to scatter the light from LED 101,and then the light travels into the light-guiding section 204. As aresult, the luminance distribution is improved and the better visibilityis expected. Since LED 201 is placed below light-inlet 203 of board 202,the area of light-guiding section 204 can be smaller as well as thesurface lighting device can be further downsized than the device whereLED 201 is disposed on the lateral side of board 202.

Light-emitting-section 205 emits the light outside fromlight-guide-board 202. One face thereof is light-emitting face 208 thatemits the light outside, and an end of the other face is scatteringsection 206 having scattering pattern 207 thereon. Scattering pattern207 are dots formed on the lower face of light-emitting-section 205 andpainted with an ink ranging between milky-white and white. Scatteringdots are formed so that the dot area becomes greater at a longerdistance from LED 201 as shown in FIG. 38. The light incident onlight-emitting-section 205 has more luminance at closer distance to LED201, thus the distribution of the printed area of scattering dots can bechanged, so that even luminance distribution of light-emitting-face 208is achievable.

The material and manufacturing method of scattering pattern 207 are thesame those discussed in the first embodiment.

Light-guiding-section 204 widens to form V-shape from end sections “q”and “m” toward corresponding corners “p” and “q”.

Reflecting layer 209 is placed beneath scattering section 206 and has ahigh reflectance. The surface of layer 209 is made of white filmincluding titanium oxide.

Diffusion layer 202 disposed on light-emitting-section is made ofsemi-transparent film finely textured, and scatters the emitted light toimprove uneven lumnance.

Holder 211 for accommodating light-guide-board 202, reflecting layer 209and diffusion sheet 210 at desirable places is made of resin because offlexibility of shape and easiness for mass manufacturing. ABS resin orpolycarbonate resin are preferable, and a color, such as white, having ahigh reflection rate is preferable.

LED 201 is mounted on circuit board 212 which holds holder 211 at agiven position to regulate the place of LED 201 just under light-inlet203.

An operation of the surface lighting device as structured above isdemonstrated hereinafter. First, the light from LED 201 enters toincident plane of light-inlet 203. Then the light is reflected on thereflecting plane, and most of the light has an angle componentsatisfying conditions of total reflection at an interface between board202 and air, so that this light is guided inside the board 202. Thelight incident on board 202 is reflected on light-guiding section 204,then guided toward light-emitting section 205. In light-emitting section205, the light guided by guiding-section 204 is totally reflected andshielded efficiently; however, the light striking scattering pattern 207on the lower face of section 205 is reflected randomly in diversedirections or travels through. The light having an angle greater thanthe critical angle at the total reflection runs out of board 202. Somelight arrives at emitting face 208, and then is emitted. Some otherlight strikes reflecting layer 209 and holder 211, and then is reflectedand returned inside of the light-emitting-section 205 again. As such,almost all the light, except some amount absorbed on the way, guidedinside board 202 is emitted from emitting face 208 for surface lighting.

As such, the light from LED 201 enters to the incident plane oflight-inlet 203, then the reflecting plane reflects this light. Thelight is then guided inside light-guide-board 202. This structure canreduce the area of light-guiding section 204. As a result, the surfacelighting device can be downsized.

In this embodiment, LED 201 is placed at a corner of board 202. Thelight from LED 201 is guided inside board 202 so that a center axis oflight distribution of the incident light can slant with respect to sides231 and 232 of board 202. This structure allows light-emitting-section205 to output luminance more uniformly, thereby realizing the surfacelighting device featuring an excellent visibility.

In this ninth embodiment, LED 201 is placed close to light-inlet 203disposed on the corner of board 202, or close to the corner oflight-emitting section 205. Regarding a first side face and a secondside face of board 202, both the faces hold light-inlet 203, the lengthof first side face is longer than that of a third side face opposite tothe first one, and the length of second side face is longer than that ofa fourth side face opposite to the second one. To be more specific, asshown in FIG. 38, the four sides of light-guide-board 202, i.e. thefirst side 231 and third side 233 opposite thereto, the second side 232and fourth side 234 opposite thereto, have different lengthsrespectively and are not parallel with each other. This structureprevents surrounding area of the LED from being outstandingly bright.This structure eliminates unnecessary sections on the light-guide-board,so that sections not contributing to irradiation on thelight-emitting-section are reduced. As a result, a surface luminousefficiency is increased.

In this embodiment, the sides 231 through 234 are all straight lines;however, they can be curved lines or have bending points. In this case,imaginary straight lines connecting “would be” corner points of board202, i.e. points “o”, “p” “q”, “m” and “l” are used for applying theconcept of the present invention.

In this embodiment, the side face containing side 232 approaches to line205 b defining light-emitting-section 205 at a greater distance from LED201, and the side face containing side 231 approaches to line 205 adefining section 205 at a greater distance from LED 201. This structureguides the light from LED 201 toward section 205 more efficiently,thereby further increasing the luminance uniformity and irradiatingsection S2 among others more efficiently. This structure allows aprojection area of light-guide-board 202 to be smaller, therebyincreasing a utilization factor of the space within the surface lightingdevice. As a result, the device can be downsized and design flexibilitycan be increased.

For a comparison purpose, a sample having the following different pointsfrom the structure discussed above is produced: the sides opposite toeach other have the same length, and the side faces opposite to eachother are parallel. This sample can reduce the size of holder, therebydownsizing the surface lighting device per se. However, the surroundingof the LED is outstandingly bright and its luminance rate R becomes aslow as not more than 0.2, which is insufficient because visibilityrecognition requires luminance rate R at least 0.3.

On the other hand, in this embodiment, LED 201 is placed away fromlight-emitting-section 205 by distance L1, thereby preventing thesurrounding of LED 201 from being too bright. Luminance rate R in thisembodiment is 0.67, which substantially satisfies the requirement ofvisibility recognition.

When another comparison is performed under the condition that thedimensions of the holders are the same, average luminance shows thefollowing difference: Luminance is measured at 36 places inlight-emitting-section 205. The sample shows its average luminance at 35cd/m², and this embodiment shows the average luminance at 40 cd/m². Thisresult proves that the ninth embodiment produces a better surfaceluminous efficiency than the sample does. Because the sample hasunnecessary sections, and the light guided into those unnecessarysections do not contribute to increasing the average luminance ofsection 205.

The ninth exemplary embodiment as discussed above, the four side facesof board 202 have different lengths with each other and are notparallel. This structure prevents the surrounding of the LED being toobright, and allows the surface lighting device per se to produce anaverage luminance at a substantially high level. Further, a number ofLEDs are reduced thereby lowering the power consumption as well assimplifying the assemble woks of mounting LEDs on a substrate. As aresult, a surface lighting device operating at a low power andeasy-to-manufacture is obtainable.

Exemplary Embodiment 10

FIG. 41 is a front view of a surface lighting device in accordance withthe tenth exemplary embodiment of the present invention. In thisembodiment, an LED, reflecting layer, diffusion layer, holder andcircuit substrate are the same as those discussed in the ninthembodiment.

Light-emitting section in this embodiment shapes in a rectangular, asshown in FIG. 41, which requires one LED to distribute the lightsufficiently in the longitudinal direction. Two sides oflight-guide-board 202 closer to LED 201 are referred to as first side231 and second side 232. An opposite side to first side 231 is referredto as third side 233, and an opposite side to second side 232 is fourthside 234. First side 231 and second side 232 are extended until theycross, and the point of this intersection is referred to as first point241. Third side 233 and fourth side 234 are extended until they cross,and the point of this intersection is referred to as second point 242. Astraight line connecting first point 241 and second point 242 forms anangle A5 with sixth side 236 connecting end point “q” of first side 231and end point “m” of second side 232. Angle A5 is approx. a right angle.This structure allows the light from LED 201 to travel in sufficientamount to the farthest place in light-emitting-section 205 from LED 201,thereby improving uneven luminance due to the rectangular of section205. Angle A5 is desirably 90 degrees, and the slant of sixth side 236can be varied by changing the positions of end points “q” and “m”. FIG.42 illustrates the changes of luminance ratio R by varying angle A5,where luminance ratio R=min. luminance/max. luminance. As shown in FIG.42, when angle A5 stays at 90 degrees, luminance rate R stands at thehighest value. Angle A5 is thus desirably approx. 90 degrees. Asdiscussed previously, from the viewpoint of visibility recognition,luminance ratio R should be not less than 55% for realizing goodcharacteristics of the surface lighting device. Angle A5 thus preferablyranges between 75 and 105 degree.

In this embodiment, all sides 231 through 234 are straight lines;however they can be curved lines or have bending points. In this case,imaginary straight lines connecting “would be” corner points of board202, i.e. points “o”, “p” “q”, “m” and “l” are used for applying theconcept of the present invention. The surface lighting device of thisembodiment (whatever shape of light-emitting-face the device has) allowsa display unit using thereof and a portable terminal using the displayunit to be small in size and consume low power as well as have excellentvisibility in the display unit.

Exemplary Embodiment 11

The surface lighting devices described in embodiments 9 and 10 areemployed in various electronic apparatuses, and the devices are used innumbers of portable terminals. In this embodiment, a portable terminalusing these surface lighting devices is demonstrated.

FIG. 39, FIG. 40 and FIG. 43 are a perspective view, a cross section anda block diagram of the portable terminal in accordance with the eleventhexemplary embodiment. A structure and an operation of this portableterminal are the same as those discussed in the fifth embodiment, thusthe descriptions thereof are omitted here.

A structure of the surrounding of display section 213 is detailed withreference to FIG. 40, which is taken along line 500—500 of FIG. 39.

Display section 213 is disposed in a part of housing 214 made of resin.Display unit 217, comprising a semi-transparent and semi-reflecting typeLCD element 215, is disposed on the surface lighting device inaccordance with the ninth and tenth embodiments. Wiring 216 for displayelement is disposed to cover LED 201 of the surface lighting device andcoupled to circuit board 212. Employing the surface lighting device inaccordance with the ninth and tenth embodiments, display unit 217realizes a small size and a low power consumption free from lowering itsvisibility. If stray light from LED 201 leaks from sections other thanlight-emitting-face 208, wiring 216 blocks almost all the leakage light,thereby improving the visibility. A display on LCD element 215 ofdisplay section 213 is seen through display-window 218 made oftransparent material. By using LCD element 215, a portable terminaloperating with a lower power and having excellent visibility isobtainable.

In this embodiment, side 231 of board 202 of which side wiring 216 isled out is not parallel with the same side 211 a of holder 211 adjacentto board 202, and side 211 a is approx. parallel with side 215 a of LCDelement 215 as is shown in FIG. 36. In order to downsize holder 211,holder 211 should have cut away on its side to be parallel with side 231of board 202; however, in such a structure, wiring 216 would not keepapprox. parallel with side 231 or the cut-away end section of holder211, and thus one end of flat wiring 216 touches the end section ofholder 211. This structure would damage wiring 216 due to vibration orother external forces. On the other hand, the structure of thisembodiment allows wiring 216 to keep contacting solidly to side 211 a ofholder 211, so that wiring 216 is scarcely damaged by vibration or otherexternal forces.

Employing the surface lighting device discussed in the ninth or tenthembodiment allows the display section of the portable terminal to reduceuneven luminance. As a result, a portable terminal with high visibilityand little recognition-errors is achievable. Since only one LED is usedin the device, the portable terminal consumes only little power.

In this embodiment, the surface lighting device discussed in the ninthor tenth embodiment is used; however, other devices discussed inprevious embodiments can be mounted to the portable terminal with thesame effects.

Exemplary Embodiment 12

FIG. 44 is a front view of a surface lighting device in accordance withthe twelfth exemplary embodiment of the present invention. FIG. 45 is across section taken along diagonal line 600—600 of FIG. 44. FIG. 29 andFIG. 46 are front views of a distribution on a scattering layer of thisembodiment.

In FIGS. 44 through 46, LED 301 can have the same structure as LED 1 orLED 20. Light-guide-board 302 can be also made of the same material asboard 2 previously discussed.

Light-guide-board 302 comprises light-inlet 303, light-guiding section304 and light-emitting section 305. The dotted line connecting corners“r” and “n” of emitting section 305 defines an interface betweenlight-guiding section 304 and light-emitting section 305 as shown inFIG. 46.

Light-inlet 303 guides the light inside light-guide-board 302. When LED301 is disposed below light-guide-board 302, light-inlet 303 is formedby an incident plane and a reflecting plane which reflects incidentlight to emitting section 305. This reflecting plane is a slope on anend face of board 302 and is disposed approx. just above LED 301. Thisstructure allows the light-inlet to scatter the light from LED 301, andthen the light travels into the light-guiding section 304. As a result,the luminance distribution is improved and the better visibility isexpected. Since LED 301 is placed below light-inlet 303, the surfacelighting device can be further downsized.

In FIG. 45, light-emitting-section 305 emits the light outside. One facethereof is light-emitting face 308 that emits the light outside, and anend of the other face is diffusion section 306 comprises scatteringlayer 307 and optical smoothing section 309. Scattering layer 307 areprinted dots and formed so that the area occupied (hereinafter referredto as “occupied area rate”) by scattering layer 307 becomes greater at acloser distance to corners “n” and “r” of light-emitting-section 305from the center of layer 307 as is shown in FIG. 46. This structureallows light-emitting-face 308 to distribute the light evenly. As aresult, a surface lighting device with excellent visibility isachievable. At the same time, the light can be used more efficiently, sothat the power consumption by the device can be reduced.

In this embodiment, as shown in FIG. 46, diagonal line C oflight-reflecting and diffusion section 306 and two straight lines D, Edisposed parallel to, equidistant from and on both sides of line C aredefined. Areas occupied by scattering layer 307 near lines D and E areapprox. equal to each other. The area of scattering layer 307 increasesat a greater distance from diagonal line C. This structure allowslight-emitting-face 308 to emitte the light more evenly, therebyrealizing a surface lighting device with excellent visibility. Further,the light is used more efficiently, so that the device consumes lesspower.

In FIG. 29, scattering layer 307 is disposed equidistantly from diagonalline C and LED 301 so that the areas occupied by scattering layer 307can be equal to each other. Further, scattering layer 307 is disposed sothat occupied area increases at a greater distance from LED 301.

In this embodiment, light-reflecting-and-diffusion section 306 is aquadrilateral and thus diagonal line C is defined. However, when section306 is a polygon or a circle, a line separating the occupied areaequally is found and defined as diagonal line C, thereby applying thesame design as discussed above.

In the case that the light enters from a corner of light-guide-board302, the outgoing light tends to grow brighter at a section nearlight-inlet 303 and at a section near diagonal line C. In order toovercome this problem, the following measures already described in thisembodiment are taken.

-   -   (1) Scattering layer 307 is placed so that the occupied areas        become equal at an approx. same distance from diagonal line C;    -   (2) Scattering layer 307 is placed so that the occupied area        increases at a greater distance from diagonal line C; or    -   (3) Scattering layer 307 is placed so that the occupied area        increases at a greater distance from LED 301.

Those measures can compensate the light amount reduced at the end oflight-emitting-section 308 by increasing the occupied area, and thusluminance distribution on light-emitting-face 308 becomes uniform. Morepreferably, combining those measures would produce the better effect.

The way of forming scattering layer 307, the material and shape thereofare the same as that discussed in the first embodiment. Layer 307 is notlimited to a circular shape but it may be a polygon or a straight line.Light-reflecting-and-diffusion section 306 as a whole is not limited toone type of pattern, but various shapes can be combined.

Scattering layer 307 is formed by screen-printing; however, the layer307 can be processed by machine-cutting or laser processing, so thatfine peaks and valleys yet rough enough for reflecting and diffusing theincident light can be formed on the lower face of light-guide-board 302.On an injection mold of the light-guide board, rough face, peaks andvalleys, or V-shaped grooves can be formed by etching or other methods.

Scattering layer 307 can be also made of separate material and placedclose to the end face of board 2.

An operation of the surface lighting device as structured above isdemonstrated hereinafter. First, the light from LED 301 enters tolight-guide plate 302 through light-inlet 303. Most of the light has anangle component satisfying conditions of total reflection at aninterface between resin and air, so that this light travels inside theboard 302 by repeating total reflections. The light guided by totalreflection is shielded efficiently; however, the light strikingscattering section 307 on the lower face of light-emitting-section 306is reflected randomly in diverse directions or travels through. Only thelight having an angle greater than the critical angle at the totalreflection runs out of board 302. Some light out of the light emittedfrom section 308 strikes reflecting sheet 309 and holder 311, and thenis reflected and returned into light-emitting-section 305 again. Afterthat, the light is emitted again from the light-emitting-face again. Assuch, almost all the light, except some amount absorbed on the way,guided into board 302 is emitted from emitting face 308 for surfacelighting.

In this embodiment, LED 301 is placed near a corner of light-inlet 303,so that some light, out of the LED light, having strong relativeintensity around P2 in FIG. 47 irradiates section S2 shown in FIG. 44.As a result, a surface lighting device having only little unevenness inluminance and excellent visibility is achievable.

Light-inlet 303 is formed by a curved face, of which cross section isarc, parallel to emitting-face 308, so that the light around P1 in FIG.47 having strong relative intensity is distributed for irradiatingsection S2. This structure allows the LED light incident on section S1of light-reflecting-diffusion section 306 to reduce its ownlight-intensity-distribution, thereby achieving uniform surfaceluminance. As a result, a surface lighting device having excellentvisibility is obtainable.

When light-guide-board 302 is formed in a symmetrical shape, e.g. asquare, scattering layer 307 is placed on diagonal line C of section 306so that the scattering pattern becomes symmetrical with respect to lineC. This structure produces surface luminance more uniformly.

In the case that light-guide-board 302 is formed in a symmetrical shape,e.g. a square, if diagonal line C of light-reflecting-and-diffusionsection 306 is placed on a diagonal line (not shown) of board 302, i.e.these two lines are approx. on the same line,light-reflecting-and-diffusion-section 306 functions most efficientlyand produces a better luminance distribution thereof.

The structure discussed above reduces luminance difference betweensection S2 in FIG. 44 and section S1 being irradiated by mainlyrelatively intensified light, so that luminance distribution isimproved. This structure produces luminance ratio R=at least 0.5. Thisstructure also realizes a relative light intensity of the lightirradiating section S2 vs. that of S1 being not less than 70%. Thisproves that the visibility of the surface lighting device is improved.

A sample light-guide-board in accordance with this twelfth embodiment isproduced having the scattering dots structured as follows: A dot on thescattering layer closest to the diagonal line is 0.4 mm in diameter,another dot farthest from the diagonal line is 0.8 mm in diameter, and aclearance between the adjacent dots is 1 mm. One green GaN LED is used,emitting face is a square of which side measures 30 mm long,light-guiding-route length L1 is 3 mm, and a thickness of thelight-guide-board is 1 mm. Electric current in the LED is 10 mA.Luminance distribution of this surface lighting device having thestructure discussed above is measured, and resultant R is 0.68. Inactual, luminance distribution is so improved that it is rarely seen onthe device viewed through an LCD element. This embodiment proves thatthe surface lighting device with extraordinarily excellent visibility isrealized.

As this discussed above, the 12th embodiment proves that the surface ofthe device emits the light more uniformly than conventional devices, anduses the light more efficiently, thereby obtaining the surface lightingdevice operating at less power.

1. A surface lighting device comprising: a light-guide-member including:a light-inlet plane; an inclined light reflecting plane above said lightinlet plane for directly reflecting light entering through said lightinlet plane; a light-guiding-section; a light-emitting-plane and sideplanes extending from opposite sides of the light reflecting plane; anda light source disposed on a corner of said light-guide-member, whereinan angle formed by said side planes of said light-guide-member, wheresaid light-inlet plane exists between the side planes, is an acuteangle.
 2. The surface lighting device as defined in claim 1, wherein atleast one of the two planes approaches a emitting face at greaterdistance from said light source.
 3. The surface lighting device asdefined in claim 1 further comprising a diffused reflection boarddisposed parallel to said light-emitting-section.
 4. The surfacelighting device as defined in claim 2, wherein at least one of the twoplanes approaches a emitting face at greater distance from said lightsource.
 5. The surface lighting device as defined in claim 1, whereinsaid light-inlet plane includes an end face slant with respect to saidlight-emitting-section and an incident plane, and said light source isdisposed on an opposite side of said end face, where said incident faceexists in-between.
 6. The surface lighting device as defined in claim 5,wherein the end face of said light-inlet plane comprises a curved facewidening in sector shape from near said light source.
 7. The surfacelighting device as defined in claim 1, wherein said light source is alight-emitting-diode having a substantially concave face.
 8. The surfacelighting device as defined in claim 1, wherein said light source is asingle piece of light-emitting-diode.
 9. The surface lighting device asdefined in claim 1, wherein the light-emitting-diode comprises aplurality of light emitting elements.
 10. A surface lighting deviceaccording to claim 1 wherein two sides of said light-guiding-section arealong two sides of said light-emitting-plane.
 11. A surface lightingdevice according to claim 10, wherein said two sides of said lightguiding section form a “V” shape.
 12. A display unit comprising: aliquid crystal display element; and a surface lighting devicecomprising; a light-guide-member including: a light-inlet plane; aninclined light reflecting plane above said light inlet plane fordirectly reflecting light entering through said light inlet plane; alight-guiding-section; a light-emitting-plane and side planes extendingfrom opposite sides of the light reflecting plane; and a light sourcedisposed on a corner of said light-guide-member, wherein an angle formedby said side planes of said light-guide-member, where said light-inletexists between the side planes, is an acute angle.
 13. The display unitas defined in claim 12, wherein said light source is disposed on a sidewhere a wiring of the liquid crystal display element is led out.
 14. Thesurface lighting device as defined in claim 12, wherein two sidesadjacent to said light source are longer than other sides respectively.15. The surface lighting device as defined in claim 12, wherein saidlight source includes at least one light-emitting-element.
 16. Aportable terminal comprising: a liquid crystal display element; and asurface lighting device comprising; a light-guide-member including: alight-inlet plane; an inclined light reflecting plane above said lightinlet plane for directly reflecting light entering through said lightinlet plane; a light-guiding-section; a light-emitting-plane and sideplanes extending from opposite sides of the light reflecting plane; anda light source disposed on a corner of said light-guide-member, whereinan angle formed by said side planes of said light-guide-member, wheresaid light-inlet exists between the side planes, is an acute angle. 17.A portable terminal comprising: a surface lighting device comprising: alight-guide-member including: a light-inlet plane; an inclined lightreflecting plane above said light inlet plane for directly reflectinglight entering through said light inlet plane; a light-guiding-section;a light-emitting-plane and side planes extending from opposite sides ofthe light reflecting plane; and a light source disposed on a corner ofsaid light-guide-member, wherein an angle formed by said side planes ofsaid light-guide-member, where said light-inlet exists between the sideplanes, is an acute angle, and a liquid crystal display element.
 18. Asurface lighting device comprising: a light-guide-member including: alight inlet plane on a bottom of said light-guide-member; an inclinedlight reflecting plane above said light inlet plane; alight-emitting-plane on a top of said light-guide-member; and sideplanes extending from opposite sides of the light reflecting plane; andwherein an angle formed by a corner of said light-guide-member where theinclined light reflecting plane is disposed is less than an angle of anopposite corner of said light-guide-member.
 19. A surface lightingdevice according to claim 18, further comprising a light source disposedat said corner of said light-guide-member.